The generally accepted, though unconfirmed, identification of the macular pigment of the human retina, as lutein, is based solely on optical spectra obtained nearly 40 years ago. Our aim is to provide an accurate and reliable identification through the use of a) UV-VIS spectroscopy, b) high pressure liquid chromatography (HPLC), c) mass spectrometry (MS) and d) chemical derivatization of the pigment followed by HPLC and/or MS. Our preliminary experiments indicate for the first time that the macular pigment may be a mixture of 2 xanthophylls - zeaxanthin and lutein, the former being in the greater abundance. This important new result, if confirmed, will provide the appropriate starting point for theories concerning the biochemical role of the pigment and for determining its metabolic origin and/or dietary source. A recently proposed theory is that the macular pigment protects retinal tissue against photosensitized oxidation by singlet oxygen. This would require the close proximity of the pigment and the vulnerable retinal structures. In order to deduce the structures involved, we will compare high resolution spectra of the pigment, measured in vivo by a psychophysical technique, with those obtained in chemical environments closely resembling those in the retina. Of particular interest will be a lipid liposome environment, similar to that provided by the membranes of Henle's fiber layer. We have recently shown that incorporation of pigment molecules into these membranes provides explanation for the polarization figure known as Haidinger's brushes. The detectibility of this figure by patients has been linked with certain ocular anomalies and diseases of the retina. The inference is that such diseases may be related to a loss of membrane protection arising from the absence of the macular pigment in the patient's eye.